How to Manage Pests
UC Pest Management Guidelines
COMMON GROUNDSEL. Common groundsel, a winter annual weed found throughout most of California except the southern desert area, may cause problems all year in the cooler coastal areas. Groundsel seeds cannot successfully germinate and grow unless they are in the top 0.5 inch of soil, so certain cultural practices can be helpful in weed management. Preplant irrigation to germinate seeds and a shallow cultivation just before planting will limit populations somewhat. This program can be augmented by throwing a dry, dust mulch along the seed row while carrying out the first cultivation. Deep plowing with a moldboard plow and inverting soil to 16 inches deep can bury many of the viable groundsel seeds. Rotate cole crops with other crops so that herbicides that effectively control this weed can be used.
PRICKLY LETTUCE. Prickly lettuce, a common winter weed in the Central Valley and southern desert area, germinates after fall irrigations or with the onset of winter rains. Napropamide and oxyfluorfen will control prickly lettuce.
COMMON PURSLANE. Be sure to remove uprooted purslane plants from the wet soil surface as they will reestablish and continue to grow if not removed.
ANNUAL SOWTHISTLE. Annual sowthistle, a widely distributed weed commonly germinating from late fall to early spring, can be controlled with napropamide or oxyfluorfen. Preplant cultivations, a dry soil mulch thrown over the seed, and deep plowing and inverting the soil to a depth of 16 inches (40 cm) will provide some control.
MUSTARDS. Mustard weeds, including London rocket and shepherd's-purse, are in the same family as cole crops, and thus are very difficult to control with herbicides. If infestations of mustards are heavy, rotate to a crop in which mustards can be easily controlled with herbicides.
NUTSEDGES. Nutsedges are summer weeds favored by moist soil and warm, sunny conditions. The tubers are easily carried in soil on farm equipment. No herbicides are available to control nutsedge in cole crops. The best strategy is to plant cole crops in infested fields during cool weather when nutsedge is not a problem, and during summer plant other crops, such as tomatoes, beans, and potatoes, in which some control of nutsedge can be achieved with herbicides. Another possibility in coastal areas is to rotate to a crop, such as strawberry, that receives preplant fumigation.
Cultivation is the only method available for removing nutsedge during cole crop growth. Cultivate before the weed has four or more true leaves or tubers will be produced; these tubers can infest susceptible crops that follow. Deep plowing 10 to 12 inches with moldboard plows can reduce nutsedge populations by 95 to 98%; however, tubers must be left deeply buried for at least 2 years for this method to be effective.
CHEESEWEED. Cheeseweed, also known as little mallow, is a very competitive weed in cole crops. It is common in the coastal areas and the desert winter production regions. It germinates from 1 to 2 inches deep, which allows it to escape preemergent applications. Nitrogen surface applications are very effective when used postemergence on cheeseweed plants in the cotyledon to 2-leaf stage. A preplant treatment of oxyfluorfen (Goal) plus a surfactant is effective against this weed; a postemergent application of the GoalTender formulation of oxyfluorfen in broccoli or cauliflower can also be effective in controlling this weed.
BURNING NETTLE. Burning nettle is a prolific seed producer and can infest cole crops in all regions. Its offensive action on workers' skin make thinning or weeding quite difficult, increasing the cost of these operations. Preplant incorporated applications of trifluralin or oxyfluorfen will effectively control it.
CHICKWEED. Chickweed is a winter annual weed that is very competitive with seedling cole crops if not controlled. Preplant incorporated applications of napropamide are effective in its control.
UC IPM Pest Management Guidelines: Cole Crops